When the backgrind tape is pulled off the upper surface of an integrated circuit, pieces of the top dielectric layer may be pulled out causing ripouts which decreases yield. In addition when backgrind tape is pulled off the upper surface of an integrated circuit to which another device has been bonded prior to backgrind, the device may stick to the backgrind tape and be removed.
An integrated infrared (IR) sensor chip with a sensor cover 34 which is attached with adhesive to the top surface of the integrated infrared sensor chip is used to illustrate a conventional backgrind process but an integrated circuit with another device attached to the surface prior to backgrind may also be used. The integrated infrared (IR) sensor in FIG 1 consists of sensors 24 and 26 which are embedded within dielectric layers 28 over the semiconductor substrate 20 and whose electrical characteristics change in proportion to the amount of incident IR radiation. The IR detection devices 24 and 26 may be thermocouples. In a typical integrated IR sensor, some of the IR detection devices 24 may be suspended over a cavity 22 to thermally isolate them from the thermally conductive substrate 20. Other IR detection devices 26 may be thermally coupled with the thermally conductive substrate 20 to be used as controls. The IR detection sensitive device 26 that is thermally coupled to the substrate remains at the substrate reference temperature whereas the IR detection device 24 suspended above the cavity and thermally decoupled from the substrate either increases or decreases in temperature as the IR radiation intensity either increases or decreases.
A dielectric layer 28 such as silicon dioxide or silicon nitride or multiple layers of one or both covers the integrated IR sensor chip. Via openings 30 filled with a metallic material provide electrical contact to the substrate 20. Etchant openings 32 that extend through the dielectric 28 over the cavity 22 enable etchant to reach the substrate 20 and to etch the substrate 20 forming a cavity 22 which thermally isolates sensor 24 from the substrate 20. A sensor cover 34 may be attached to the integrated IR sensor chip over the openings 32 to prevent solvents and debris from subsequent processing steps such as backgrind and wafer sawing from getting into the cavity. The sensor cover 34 may be an epoxy film which is laminated to the surface of the integrated sensor chip.
A typical backgrind process to thin the substrate 20 is shown in FIGS. 2A and 2B. As shown in FIG 2A, backgrind tape 36 is applied to the topside of the wafer containing the integrated sensor chip to hold the wafer in place during the backgrind process. After the substrate 20 is background to a specified thickness, the backgrind tape 36 is removed by carefully peeling it off. As shown in FIG 2B, in some instances the window cover 34 may also come off during this tape removal process decreasing yield. In addition, the etchant holes 32 through the dielectric that is suspended above the cavity 22 reduce the strength of the dielectric making it more fragile. On occasion, part of the dielectric 38 may also break off and be removed along with the backgrind tape during the detaping process. When the dielectric 38 breaks, rework to salvage the sensor to preserve yield is impossible.